Filling connection hole with wiring material by using centrifugal force

ABSTRACT

A method of manufacturing a semiconductor device includes the steps of: preparing a substrate having an insulating layer with a connection hole; forming a wiring layer covering the connection hole; and heating the substrate to a temperature equal to or higher than a temperature of fluidizing the wiring layer material and rotating the substrate in a direction of generating centrifugal force directing from an opening of the connection hole toward the bottom of the connection hole. The centrifugal force facilitates reflow of the wiring layer so that the inside of the connection hole can be more preferably filled and the surface of the wiring layer can be planarized.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relates to techniques of filling a fine contacthole in an insulating layer with wiring material of a wiring layer forthe electrical connection between the wiring layer and an underlyinglayer having a conductive surface.

b) Description of the Related Art

For the electrical connection between an impurity doped layer and awiring layer over the doped layer or between multi-wiring layers ofsemiconductor devices, generally a connection hole (e.g. contact hole,via hole) is formed in an insulating layer formed between two layers tobe electrically connected, and the connection hole is filled with wiringmaterial. If the connection hole is filled insufficiently, contactfailure may occur.

In order to have a good manufacture yield of semiconductor devices, inaddition to properly filled connection holes, the wiring layer after thehole filling process is required to have as flat a surface as possiblewithout leaving irregular surfaces. For planarization, a conventionalhole filling process uses an etch-back process, an Al reflow sputteringprocess, and other processes.

An etch-back process is a combination of a conventional film formingprocess such as sputtering, and an etching process. With this process,wiring material is first deposited thicker than a final wiring layer, bysputtering or other processes. Thereafter, the surface of the wiringlayer is planarized by coating material with fluidity such asphotoresist. After this photoresist is thermally set, it is dry-etcheduniformly from the surface thereof to remove irregular surfaces andobtain a final planarized wiring layer.

An Al reflow sputtering process can be used when Al or Al alloy is usedas wiring material. This process sputters wiring material at a substratetemperature at which Al can be fluidized. Since the sputtered film hasfluidity, the wiring material flows from convexities to concavities toplanarize the wiring layer surface. As compared to usual sputtering, thehole filling performance can be improved, and in addition, planarizationis performed at the same time.

As semiconductor devices are becoming highly integrated, the diametersof connection holes are becoming small. An aspect ratio of a depth to adiameter of a connection hole tends to increase. Not only with usualsputtering but also with Al reflow sputtering, the larger is the aspectratio of a connection hole, the worse is the step coverage of a formedwiring layer and the more difficult is the process of properly fillingthe connection hole.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofmanufacturing a semiconductor device capable of filling a connectionhole in a good filled state.

It is another object of the present invention to provide a semiconductordevice manufacturing system capable of filling a connection hole in agood filled state.

According to one aspect of the present invention, there is provided amethod of manufacturing a semiconductor device comprising the steps of:preparing an underlying substrate having a conductive region; forming aninsulating layer on the substrate, the insulating layer having aconnection hole at a position corresponding to the conductive region;forming a wiring layer covering the connection hole; and heating thesubstrate and rotating the substrate in a direction of generatingcentrifugal force directing from an opening of the connection holetoward the bottom of the connection hole to reflow the wiring layer.

According to another aspect of the present invention, there is provideda semiconductor device manufacturing system comprising: a hermeticallysealed chamber capable of being evacuated; semiconductor substrateholding means rotatively mounted in the hermetically sealed chamber andhaving a holding surface for holding a semiconductor substratesubstantially perpendicular to a rotation radius direction; drivingmeans for rotating the semiconductor substrate holding means; andsemiconductor substrate heating means for heating the semiconductorsubstrate held by the semiconductor substrate holding means.

After wiring material is deposited to cover an insulating film with aconnection hole, the substrate is heated to a temperature allowing thewiring material to be reflowed, and rotated to apply centrifugal forceto the wiring layer with fluidity. Since this centrifugal force isgenerated in the depth direction of the connection hole, the fluidizedwiring material becomes easy to flow toward the bottom of the connectionhole and to fill the concave space in the connection hole.

As above, a connection hole can be properly filled with wiring materialby using a simple hole filling system, and at the same time the wiringlayer can be planarized satisfactory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are cross sectional views of a semiconductor device,illustrating a process of filling a contact hole according to anembodiment of the invention.

FIGS. 2A and 2B are cross sectional views of semiconductor devicesaccording to an embodiment of the invention.

FIG. 3 is a diagram showing the structure of a semiconductor devicemanufacturing system according to an embodiment of the invention.

FIG. 4 is a diagram showing the structure of a semiconductor devicemanufacturing system according to another embodiment of the invention.

FIGS. 5 and 6 are cross sectional views of semiconductor devicesaccording to other embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described with reference to theaccompanying drawings.

Embodiments will be described by using an example of filling a contacthole for the electrical connection between a source/drain region of ametal oxide semiconductor (MOS) transistor and a wiring layer.

FIG. 2A is a cross sectional view of a MOS transistor under manufactureprocesses. Referring to FIG. 2A, in the upper region of an Si substrate1, a p-/n-well region 2 having a predetermined impurity concentration isformed. On the well region 2, a gate oxide film 3 and a gate electrode 4are formed. Side spacers 5 made of SiO₂ film are formed on the sidewalls of the gate oxide film 3 and gate electrode 4. In the well surfaceregions on both sides of the gate electrode, high impurity concentrationregions 7 are formed which are served as source/drain regions having aconductive type opposite to the well region 2. Surrounding thistransistor structure, a field oxide film 6 is formed by a thick SiO₂film.

Covering these transistor and field oxide film, an interlayer insulatingfilm 8 such as a phosphosilicate glass (PSG) film or aborophosphosilicate glass (BPSG) film is formed. Contact holes 9 areformed in the interlayer insulating film 8 for the electrical connectionbetween the lower high impurity concentration regions 7 and an upperwiring layer to be later formed. These processes may use conventionalMOS transistor manufacture processes.

FIG. 2B is a schematic cross sectional view showing the region near thecontact hole 9 of the interlayer insulating film 8 exposing the highimpurity concentration region 7. The following description relies onthis drawing of FIG. 2B. For example, the thickness of the interlayerinsulating film 8 is about 700 nm to 1 μm, and the diameter of thecontact hole is about 0.5 μm.

The processes to follow are performed, for example, by a semiconductordevice manufacturing system shown in FIG. 3, including a sputteringsystem S, a substrate transport system T, and a hole filling or reflowsystem R.

First, a wiring layer is formed covering the interlayer insulating film8, by using the sputtering system S shown in FIG. 3. As shown, thissputtering system is a DC magnetron sputtering system having an uppercathode 21 on which a sputtering target 22 is mounted and a susceptor(counter electrode) on which a substrate 24 is mounted facing the target22. The substrate 24 is heated to a predetermined temperature with aheater 25 equipped in the susceptor. The interior of the sputteringchamber is maintained to have a predetermined pressure and atmosphere bya vacuum pump 26a and an unrepresented gas supply system.

Wiring material used is those materials having a relatively low meltingpoint, for example, Al and Al alloy such as Al/Si/Cu and Al/Cu. Forexample, in sputtering an Al/Si/Cu layer, an Al/Si/Cu alloy sputteringtarget is used under the conditions of an Ar atmosphere, a pressure of 2mTorr, a DC power of 10 kW, a film forming speed of 1 μm/min, and asubstrate temperature of about 200° C. A wiring layer is formed to athickness of, for example, about 800 nm.

An example of the configuration of a wiring layer is shown in FIG. 1Aand indicated by reference numeral 10. As compared to a thickness of thewiring layer 10 formed on the flat surface of the interlayer insulatingfilm 8, a thickness at the side wall of a contact hole is thin. Aconcave shape is likely to be left in the contact hole, and insufficientfilling of the contact hole is likely to occur. With such insufficientfilling of the contact hole, good electrical connection between thewiring layer 10 and high impurity concentration region 7 is oftendifficult to be obtained. The concave shape of the wiring layer left inthe contact hole makes it difficult to pattern a film to be formed onthe wiring layer.

In order to improve the filling state of the wiring layer, a reflowprocess is further performed by using the reflow system R shown in FIG.3.

The substrate with the wiring layer is transported into the reflowsystem R having a substrate heating unit 33, a substrate rotating unit32, and a vacuum pump unit 26c. Although the substrate may betransported from the sputtering system S to the reflow system R underatmospheric conditions, it is desired that as shown in FIG. 3, thesubstrate is transported by the substrate transport system T at areduced pressure or in an inert gas atmosphere. Transportation of thesubstrate at a reduced pressure or in an inert gas atmosphere preventsthe surface oxidation of Al or Al alloy and allows reflow to beperformed smoothly.

A chamber 28 of the substrate transport system T, the sputtering chamber23, and a chamber 30 of the reflow system R are coupled via gate valves27a and 27b which are adapted to be opened and closed. A vacuum pump 26bis coupled to the chamber 28 to maintain a reduced pressure state of thechamber 28. When the substrate is transported from the sputtering systemS to the substrate transport system T, the inside of the chamber 28 isadjusted to have the same pressure as the sputtering chamber 23.Thereafter, the gate valve 27a is opened and the substrate 24 in thesputtering system S is transported into the substrate transport system Tby a substrate transport robot 29 having a support arm which can beexpanded, contracted, moved up and down, and rotated. After thistransportation, the gate valve 27a is closed.

The substrate transportation from the substrate transport system T tothe reflow system R is performed in a similar manner. After the insideof the reflow chamber 30 is adjusted to have the same pressure as thesubstrate transport chamber 28, the gate valve 27b is opened. Thesubstrate transport robot 29 expands the support arm and places thesubstrate 24 held by the arm on a substrate holder mounted on the innerwall of a rotary drum 31 of the reflow system R. Thereafter, thesubstrate transport robot 29 contracts its arm to retract it in thesubstrate transport chamber 28, and the gate valve 27b is closed.

The rotary drum 31 in the chamber 30 of the reflow system R has arotation radius of, for example, about 10 to 50 cm. The substrate 24 isheld by the substrate holder mounted on the inner wall of the rotarydrum 31. The rotary shaft of the rotary drum 31 is rotated by a motor 32installed outside of the reflow system R. The axis of the rotary shaftis in the horizontal direction in this embodiment. The surface of thesubstrate held by the substrate holder faces the rotation center of therotary drum 31, with the rotation radius coinciding with the normal tothe substrate surface.

The vacuum pump 26c coupled to the reflow chamber 30 can maintain theinside of the chamber 30 in a reduced pressure atmosphere. The reducedpressure atmosphere of the reflow chamber 30 is preferable in order toreduce an air flow resistance during the rotation of the rotary drum 31and suppress the oxidation of wiring material. Although not representedin FIG. 3, gas such as Ar and N₂ may be supplied from a gas supplysystem to the chamber 30. For example, the inside of the reflow chambermay be maintained in an inert gas atmosphere of Ar, N₂ or the like. Inorder to improve a reflow performance, it is preferable to maintain theinside of the reflow chamber 30 in a highly evacuated state of 1×10⁻⁷Torr or lower.

The substrate heater 33 for heating a substrate is installed, forexample, as shown in FIG. 3 at the outer circumferential area of therotary drum 31. A plurality of substrate heaters 33 may be installed toheat the substrate to a predetermined temperature. The substrate heater33 may also be mounted in the rotary drum 31.

Before the start of, or during, the reflow process using the reflowsystem R, the substrate temperature is set to a temperature from about350° C. to about 600° C. by considering the fluidizing temperature ofwiring material Al/Si/Cu, and more preferably to a temperature fromabout 400° C. to about 600° C. The rotation speed of the rotary drumduring the reflow process is set to a value from about 10 rpm to about100,000 rpm, more preferably from about 100 rpm to about 100,000 rpm.For example, the rotation speed of the rotary drum 31 may be set to avalue from about 10 rpm to about 10,000 rpm or from about 100 rpm toabout 10,000 rpm.

The state of the wiring layer in the contact hole during the reflowprocess is shown in FIG. 1B. Arrows a indicate the direction ofcentrifugal force generated while the substrate is rotated in the reflowsystem R. The centrifugal force is applied uniformly over the whole areaof the substrate in the depth direction thereof.

A heated and fluidized wiring layer tends to flow downward by theinfluence of gravitational force. This flow is not necessarily smooth ifviscosity of the layer is rather high. Fluidity may be enhanced byraising the substrate temperature and lowering the viscosity of thewiring material. However, a raised substrate temperature is oftenundesirable because a problem of surface oxidation, Al migration, orothers may occur.

In the above embodiment, however, centrifugal force far greater thangravitational force is applied to a fluidized wiring layer, so thatdownward fluidity of the wiring layer can be enhanced without raisingthe substrate temperature too high.

As illustrated in FIG. 1B, fluidized wiring material becomes easy toflow in the direction of centrifugal force and the trench left in thecontact hole 9 can be buried preferentially. At the final stage such asshown in FIG. 1C, the inside of the contact hole is completely filledand the surface of the wiring layer 10 is planarized.

In order to improve the reflow performance for a contact hole, it isnecessary to apply centrifugal force components from an opening of thecontact hole toward the bottom, preferably in coincidence with the depthdirection of the wiring layer. Centrifugal force is generated outwardfrom the rotation center, i.e., along the axis perpendicular to thetangent plane of a rotation circumference. It is therefore preferable tomake the normal to the substrate surface be coincident with the rotationradius direction.

It is expected that this flow is effective also for removing voids, ifany, in the wiring layer filling a contact hole, immediately after theformation of the wiring layer. Such voids are formed during the filmforming process so that they are usually at a reduced pressure whichcorresponds to the reduced pressure atmosphere maintained during thefilm formation. It is considered that the fluidized wiring layer appliedwith centrifugal force crashes these reduced pressure voids and inertgas in the voids is dissolved in the nearby wiring layer.

Alternatively, it is considered that the wiring material over a voidflows in the contact hole by centrifugal force to open the upper wall ofthe void and this recess of once the void is filled with the wiringmaterial.

The sputtering system, substrate transport system, and reflow system arenot limited to the structure shown in FIG. 3. An example of anothersystem structure is shown in the plan view of FIG. 4 which has a reflowsystem having a different rotation direction from that shown in FIG. 3.The substrate rotation axis of the reflow system R shown in FIG. 4extends in a vertical direction different by 90 degrees from that of thereflow system R shown in FIG. 3. Obviously, either of the rotation axesmay be applied.

In FIG. 4, the sputtering system S and reflow system R are disposedaround the substrate transport system T and connected thereto. Aplurality of different systems may be connected around the substratetransport system T. The substrate transport system T transports asubstrate to and from the sputtering system S and reflow system R in themanner similar to the system structure shown in FIG. 3.

In this structure of the reflow system having a vertical rotation axisof the rotary drum, a substrate transport chamber for accommodating asubstrate transport cassette may be provided at the upper or lower areaof the rotary drum. In this case, a substrate transported by thesubstrate transport system T is loaded in the substrate transportcassette, and the cassette is moved upward or downward to place thesubstrate on a substrate holder on the inner wall of the rotary drum.

In the above embodiments, the film forming system and the reflow systemfor performing a high temperature rotation process are independent andseparate systems. Therefore, the reflow system can be made having arelatively simple structure without making it complicated. A method offorming a wiring layer is not limitative, but any other film formingsystems may be used. In addition to a usual DC sputtering system, othersputtering systems may be used, such as high frequency sputtering andcollimation sputtering. Film forming systems such as a thermal CVDsystem and a plasma CVD system may also be used.

It is not always necessary to perform a wiring layer forming process anda reflow process by independent and separate systems, but the filmforming system itself may be provided with a rotation mechanism toperform the rotation process after or at the same time the film isformed.

In the above embodiments, the radius of the rotary drum of the reflowsystem is set in a range from about 10 m to about 50 cm and the rotationspeed is set in a range from about 10 rpm to about 100,000 rpm, e.g., ina range from about 100 rpm to about 100,000 rpm. These conditions arenot limitative. In order to improve the reflow performance for a contacthole, centrifugal force applied to the substrate during the reflowprocess is desired to be large. A centrifugal force is generally definedby mrω² where m is a mass of substance to which a centrifugal force isapplied, r is a rotation radius, andωis an angular velocity. In order toincrease centrifugal force, either the rotation radius or the angularvelocity (rotation speed) is made as large as possible.

Even if both the rotation radius and rotation speed are smaller thanthose values used in the embodiments, it can be expected that the reflowperformance can be improved if centrifugal force toward a contact holeis generated, as compared to the case the substrate is heated to atemperature sufficient for fluidizing wiring material, without applyingany centrifugal force.

It can also be expected that the reflow performance can be improved evenat a substrate temperature slightly lower than the temperature used byusual Al reflow or other processes, because centrifugal force generatedby the rotation of the substrate enhances the fluidity in the depthdirection of a contact hole.

The same effects may be expected even if the direction of generatedcentrifugal force is not coincident with the substrate depth directionso long as the centrifugal force has vector components in the depthdirection. In this meaning, the term "normal" or "perpendicular" doesnot strictly mean the exact normal or the exact perpendicular, but canbe nearly normal or nearly perpendicular provided that the generatedcentrifugal force is similar.

In the above embodiments, a single layer of Al/Si/Cu is used as thewiring layer. As shown in FIG. 5, a barrier metal layer 11 such as a WSilayer, a Ti layer, a TiN layer, and a TiON layer may be used as anunderlying layer of an Al alloy layer 10. In this case, the barriermetal layer 11 is formed to about 50 nm thick by sputtering before theAl alloy layer is formed. For example, a TiN barrier layer of 50 nmthick is formed through reactive sputtering under the conditions of anitrogen pressure in a sputtering atmosphere of 4 mTorr, a substratetemperature of 200° C., a power of 6 kW, and a target of Ti. Theprocesses to follow for forming an Al alloy layer and reflowing it aresimilar to the embodiment processes.

In the above embodiments, a contact hole is filled with wiring materialfor the electrical connection between source/drain regions of a MOStransistor and a wiring layer. The embodiment processes may be used forfilling a well contact hole with wiring material for the connectionbetween a p- or n-type well region and a wiring layer or for filling avia hole with a wiring layer for the connection between upper and lowerwiring layers of multi-wiring layers. In this specification, both acontact hole and a via hole are collectively called a connection hole. Aconnection hole in an insulating film may be formed with a taperparticularly at the upper portion of the hole, such as shown in FIG. 6.

The embodiment method is considered to become more effective, as thelarge the aspect ratio of a depth to a diameter of a connection holebecomes.

The present invention has been described in connection with thepreferred embodiments. The invention is not limited only to the aboveembodiments. It is apparent to those skilled in the art that variousmodifications, improvements, combinations and the like can be madewithout departing from the scope of the appended claims.

What is claimed is:
 1. A method of manufacturing a semiconductor devicecomprising the steps of:preparing an underlying substrate having aconductive region; forming an insulating layer on said substrate, saidinsulating layer having a connection hole at a position corresponding tosaid conductive region; forming a wiring layer covering said connectionhole in an evacuated state; while keeping the evacuated state after saidstep of forming a wiring layer, heating said substrate to enable reflowof the wiring layer and rotating said substrate in a direction ofgenerating centrifugal force in a depth direction of the substrate, thecentrifugal force being directed from an opening of said connection holetoward a bottom of said connection hole to enhance reflow of the wiringlayer.
 2. A method of manufacturing a semiconductor device according toclaim 1, wherein said wiring layer comprises Al or Al alloy.
 3. A methodof manufacturing a semiconductor device according to claim 2, whereinsaid wiring layer comprises a layer formed of at least one selected froma group consisting of WSi, Ti, TiN, and TiON, under said Al or Al alloylayer.
 4. A method of manufacturing a semiconductor device according toclaim 1, wherein at said reflow step said substrate is heated to atemperature in a range from about 350° C. to about 600° C.
 5. A methodof manufacturing a semiconductor device according to claim 1, wherein atsaid reflow step said substrate is heated to a temperature in a rangefrom about 400° C. to about 600° C.
 6. A method of manufacturing asemiconductor device according to claim 1, wherein at said reflow stepsaid substrate is rotated at a rotation speed in a range from about 10rpm to about 100,000 rpm.
 7. A method of manufacturing a semiconductordevice according to claim 1, wherein at said reflow step said substrateis rotated at a rotation speed in a range from about 10 rpm to about10,000 rpm.
 8. A method of manufacturing a semiconductor deviceaccording to claim 1, wherein at said reflow step said substrate isrotated at a rotation speed in a range from about 100 rpm to about100,000 rpm.
 9. A method of manufacturing a semiconductor deviceaccording to claim 1, wherein at said reflow step said substrate isrotated about a horizontal axis.
 10. A method of manufaturing asemiconductor device according to claim 1, wherein at said reflow stepsaid substrate is rotated about a vertical axis.